This invention relates to an x-ray diffraction crystal for analyzing long wavelength x-rays, i.e. x-rays having a wavelength of at least 50 Angstroms, and to a method of making such crystals.
X-rays having wavelengths greater than about 10 A are generally known as soft x-rays and are detected using a wavelength dispersive spectrometer with a crystal as a dispersive element. X-ray spectroscopy below 1 keV would allow identification of elements with atomic numbers below 10 and surface analysis at a depth of 10-1,000 A since soft x-ray photons occur below 1 keV, or wavelengths greater than 12.4 A.
Langmuir-Blodgett multi-layer pseudo-crystals are generally used as a dispersive element. Each layer is a monomolecular layer of a heavy metal soap. The distance between the heavy metals is determined by the chain length of the fatty acid. The distance determines the maximum x-ray wavelength which can be resolved. The heavy metal, i.e. the cation, determines the intensity of the diffracted radiation and the intensity is directly related to the atomic number of the cation.
The most commonly used pseudo-crystal is lead stearate wilth a 2d (d being the interplanar distance) spacing equal to 100 A. Longer "d" spacing crystals using lignoceric acid, and the like can be made but are extremely difficult to build.